I have some questions to biochemistry. I'm from Scandinavia and not that good in English..but I'll hope this is somewhat understandable and clear.

1. Enzymes doesn't influence equibrilium, but they lower the activation energy. I wonder how this is possible? Isn't the activation energy expressed in free Gibbs energy? If so, how can the equibrilium be unchanged? I thought delta Gibbs was the same as the distance to equibrilium.

2. Under ATP synthesis the enzym ATP synthase undergoes rotational catalysis. I understand that something is rotated, but I don't understand what. Is it a change in the seat themselves, or do they only change places among eachother?

3. Under starvation ketogen acids can deliver energy to the brain. Ok enough that the brain can make AcCoA from acetoacetate, but how can AcCoA give energy further through oxidation? I thought that there was a lack of intermediates in the citric acid cycle under starvation, unless this situation of depression only occurs in the liver. Comments appreciated.

4. How can insulin stimulate the degradation of proteins? I cannot see the logic in this statement, because, as far I can see, this will lead to a less effective removal of blood glucose as pyruvate and AcCoa from glucose will get competition from the same degradation products from proteins.

1. Yeah, the textbook says that also, but I can't truly understand why if delta G changes. Or are we maybe talking about different delta Gs?

3. I guess the point with keton bodies is to get energy when there's a lack of sugar as energy source. But how can keton bodies give energy to the brain if the intermediates of the citric acid cycle lack? Isn't the intermediates deprived to make as much blood glucose as possible?

4. Of course But isn't it better to get all energy from glucose instead? To remove as much as possible of the excess blood glucose through degradation (insulin signals that there's too much, right?). I guess if proteins are degradaded at the same time, there will be a less effective removal of glucose because of the competition.

I believe that somebody out there know some answers All help appreciated

You have very, very, very, VERY little of energy in free glucose! Something more is in glycogen, but most you have in lipids(!) and proteins. But you cannot burn all the glucose and wait, whether will it be OK. It's similar like with fire. You need to start with paper and later add wood or coal. However, you cannot wait until you burn all the paper And of course, if we talk about the start of exercise, when you have still enough energy storage molecules, you use first storage proteins, so you do not need to worry you had to break some glucose transporters or enzymes.